Under the 3GPP standards, a NodeB (or an eNB in LTE (i.e. Long Term Evolution)) is the base station via which mobile devices connect to the core network and which defines a cell of the network. Home base stations (HNB) provide short range 3G radiofrequency (RF) coverage, and are sometimes referred to as a femto access point (FAP). Where the home base station is operating in accordance with the LTE standards, the HNB is commonly referred to as an HeNB. The HNB or HeNB provides radio coverage (for example, 3G, 4G and/or WiMAX) within the home, small or medium enterprises, shopping malls, etc. and typically connects to the core network via a suitable Home eNB gateway HeNB GW and public or corporate broadband (BB) access network (for example via an ADSL link to the Internet). During operation in a normal operation mode or normal state, the HNB or HeNB enables users of a User Equipment (UE) to communicate with other such users via one of a number of the base stations (eNodeB, eNB), the HeNB GW and a core network.
In a connected or active state or mode, a UE is registered with the network and has an RRC (Radio Resource Control) connection with a base station, so that the network can identify which cell the UE belongs to and can transmit data to and receive data from the UE. In LTE, in the active state or mode, the Handover procedure allows UEs to have service continuity while moving within the Intra LTE system (Intra RAT and Inter Frequency) and towards other RATS (Radio Access Technologies).
A UE also has a power conservation or idle state or mode in which, typically, the UE is not transmitting or receiving data, and no context about the UE is stored by the base station. In the idle state, the location of the UE is known only (to the MME (Mobility Management Entity) in 3GPP) at the granularity of a Tracking Area (TA) comprising a cluster or group of base station cells. When in the idle state, a UE selects and reselects cells according to the parameters broadcast by the base station in the BCH (Broadcast Channel), with a frequency given by a Cell Reselection Timer Value, and the base station is not aware of the cell selections/reselections made by the UE. If a UE moves into a cell which is not part of the tracking area(s) it is registered with at the MME, then a tracking area update is triggered in order to inform the MME of the TA in which the UE is currently located.
Currently, in order to establish communications with a UE, a paging request is sent to all the cells of the TA(s) with which the UE is registered at the MME. This results in each HNB or HeNB operating each relevant cell sending a paging message for the UE. Generally, only the base station operating the cell in which the UE is located will receive a paging response from the UE. However, this method of paging a UE uses a significant load on the air interface because a tracking area may comprise a large number of cells, and a UE may be registered with multiple tracking areas. In such cases, the paging overhead is undesirably large.
The invention aims to alleviate the above issues.